The evolution of cellular communications has resulted in a proliferation of networks of different technologies and corresponding different air interfaces. In order to provide nearly universal coverage and a continuity of communications, wireless mobile stations have been, or are being, developed that are capable of operation in each of multiple networks, wherein each such network implements a different technology than the other networks of the multiple networks. Among the different network technologies are CDMA (Code Division Multiple Access) technologies, such as CDMA 2000 HRPD (High Rate Packet Data), that are capable of providing HRPD communication services, and conventional, or circuit switched, CDMA cellular communication technologies, such as a CDMA 3G1X.
Currently, the Third Generation Partnership Project 2 (3GPP2) standards provide a Short Data Burst (SDB) feature for 3G1X systems that permits a transfer of data frames between a packet data network and a mobile station (MS) over a traffic channel of the 3G1X network when the MS is engaged in an active voice or packet data call and over a common channel of the 3G1X network when the MS's packet data session is dormant and the MS is not engaged in a voice call. The 3GPP2 standards further provide a similar functionality for HRPD communication systems, that is, a Data Over Signaling (DOS) feature, for a transfer of ‘higher layer’ data between an HRPD network and an MS over either a common channel or a traffic channel of the HRPD network. For example, the SDB and DOS features may be used to transfer instant messaging text, email, or a web page to an MS otherwise engaged after a packet data communication session is established between the MS and the 3G1X or HRPD network, respectively.
As network operators begin deploying HRPD networks in combination with their 3G1X networks, some operators plan to allocate circuit-based, or circuit switched, services exclusively to 3G1X network resources and to transfer all packet data traffic received from or intended for the Internet via the HRPD networks. In such hybrid systems, when the MS is in the 3G1X network, for example, and is active with a circuit voice call or is idle and monitoring a 3G1X paging channel, the MS cannot exchange HRPD DOS with the Internet via the HRPD network. In order to provide such packet data to such an MS, it has been proposed, in U.S. patent application publication no. 2004/0120283, that when packet data arrives from the Internet for the MS, the HRPD network request the 3G1X network to page the MS to request that the MS move to the HRPD network so that the packet data can be delivered to the MS. Further, if an MS in the 3G1X network needs to send small amounts of data to the packet data network, the MS will have to drop its circuit call if it has one and move to the HRPD network in order to transfer the packet data. After the MS has switched to the HRPD network, when a circuit switched voice call (a 3G1X service) is received for an MS that is monitoring or active with a packet data session on an HRPD network, the MS is “cross-paged” on the HRPD network, that is, is notified, via a page from the HRPD network, of the 3G1X service. The MS must then leave the packet data session on the HRPD network (which may go dormant) and move back to the 3G1X network to accept the circuit voice call. Alternatively, an MS may be configured to return to the 3G1x after a period of time when no additional packet data is sent or received on the HRPD network. The need for an MS in a 3G1X system to switch back to the packet data network where its packet data session is anchored in order to send or receive a small amount of packet data, possibly dropping any circuit voice call in the process, then returning back to the 3G1X circuit network to resume circuit services, is inconvenient for the user of the MS and wasteful of system resources.
Therefore, a need exists for an improved method and apparatus for transferring packet data between an MS in a 3G1X network and the MS's packet data session which is anchored on a packet data network without the MS having to leave the circuit network and move back to the packet data network.